Pump timing device



Aug. 21, 1962 R. N. SULLIVAN PUMP TIMING DEVICE Filed June 18, 1959 /N VE N TOR RICHARD N. SULLIVAN 5077'0/W 0F STROKE in/M A T TORNE Y nit' tas This invention relates to fluid energy translating devices of the axial piston type which are capable of use either as motors or pumps.

More specifically, this invention relates to axial piston pumps having a reaction member in a tilted but fixed plane and including a valve plate at the output end of the pump which can be rotated to vary the output of the pump.

It is a primary object of this invention to provide, in pumps of the type described, a relief valve for limiting the pressure rise in any of the cylinders as the pistons pass over the land separating the main inlet and outlet ports.

It is a further object of this invention to provide a relief valve of the type described which has a very low inertia so that it can operate to limit pressure rise in any of the piston chambers as it passes over a land and can operate at extremely high speeds.

These and other objects of this invention will become readily apparent from the following detailed description of the drawings in which: i i i FIG. 1 is a cross section illustration of an axial piston P p;

FIG. 2 is a cross section illustration of the pump valve plate taken approximately along the line 22 of FIG. 1 with the lower portion broken away;

FIG. 2a is a bottom view of FIG. 2 illustrating the position of the flapper valve.

FIG. 3 is a cross section view taken approximately along the line 3-3 of FIG. 1; and

FIG. 4 is a graphical showing of the pump piston stroke.

Referring to FIG. 1, the pump includes a mounting pad and a drive shaft 12. The drive shaft 12 rotates a sleeve-like member 14 concentrically mounted in a sleeve bearing 16. A universal connection 18 is provided between the shaft 12 and the main rotor body 20. The main rotor body includes a plurality of pistons 22 which include a connecting rod 24 having ball joints at each end with the anti-piston end including a shoe 26 which engages the sleeve bearing 16. The piston 22 includes an annular recess 30 which receives leakage oil past the piston sides and connects this flow with a central passage 32 leading down to the opposite end of the connecting rod. This fluid is connected to an area 34 at the bottom of the shoe 26 so as to pressure balance the opposite ends of the piston-connecting-rod-shoe combination. This avoids the use of excessively large thrust bearings when the pump is Working under load. The cylinder bores exhaust at the top into a rotatable valve plate 40 which has a sealing engagement with the upper or outer face 42 at the anti-drive end of the main rotor 20. Each cylinder bore is necked down at 36 so as to provide a pressure balance with the valve plate 40 so that just sufiicient pressure exists therebetween to prevent excessive leakage. As a result, excessive loads and wear are avoided.

This valve plate 40 can be rotated, in a manner to: be described hereinafter, through a range of approximately 90 so as to actually vary the output capacity of the pump. The valve plate 40 is better seen in FIG. 2 and includes inlet and outlet annular slots 42 and 44, respectively. When the out slot of the plate aligned (as shown in FIG. 2) with all of the pistons which are generating pres- R 3,050,014 PatentedAug. 21, 1962 sure, the maximum capacity will be obtained. However, if the plate is rotated 90, some of the pistons which are at maximum pressure stroke will be dumping flow back into the pistons which are on the intake stroke. Therefore, the total output of the pump is greatly reduced.

The cylinder outlets 36, as shown in FIG. 2, are slightly smaller in length than the length of the land 48 between the ends of the inlet and outlet slots 42 and 44. Under conditions when the valve plate 40 is rotated a substantial amount (toward reduced capacity), certain of the pistons will have their respective exit ports 36 crossing the land 48 when the pistons are traveling at a maximum velocity and on a compression stroke. Thus, for example, as shown in FIG. 4, the piston stroke may be represented by the line A with the top and bottom of the stroke being represented by the peak and maximum depression of the curve A. Under normal output conditions, the pistons will pass over the lands between the inlet and outlet ports when they are at or near the peak or bottom of the curve A. In other words, the pistons pass over the lands when they. are at a minimum velocity. However, when the valve plate is rotated to reduce the pump capacity, the pistons will pass over the lands at some point, as for example, in the region B of curve A where the velocity of the piston is at a maximum. In this region, the normal pump capacity of the piston-cylinder combi nation will be at a maximum; and, therefore, when the outlet is blocked off by the land 48, the pressure rise of the fluid being worked is relatively high. As a result, hammering and excessive pressures are encountered which result in high losses. To this end, the face of the Valve plate 40 has a port 49 located in the land 48. The port 49 leads to a passage 50 which is covered by the free end 51 of a leaf spring 52 which is fixed at its other end by means of one or more rivets 53 to form a cantilevered member. When the pressure in any given cylinder port 36 exceeds that of the outlet passage 44, the valve end 51 will move away from the opening 50 and permit a flow through a drilled passage 51a leading to the pump outlet slot 44. The leaf spring valve 52 sits in a recess 54 on the outer periphery of the valve plate 40. The leaf spring valve or flapper valve 52 is substantially free to move to an open or closed position depending on the pressure difierences thereacross. Of primary importance is the fact that there is substantially no spring rate; and, of a special importance is the fact that there is very little inertia to be overcome inv the valve, whereby it is extremely fast acting. When the flapper valve moves toward valve plate 40 the fluid thereunder is squeezed out along the sides. This causes adampening reaction so that the over-all efiect reduces vibration of the flapper valve.

Thus, during a pressure stroke, as a particular outlet port 36 passes over the land 48, and as soon as the pressure in that region and the region of port 49 exceeds that of pump outlet slot 44, the end 51 of the valve 52 will open to permit a flow to the passage 51a and the slot 44. When this pressure in the passage 49 is reduced, the pressure in the slot 44 and the passage 51a act on the downstream side of the valve end 51 immediately closing the valve.

The position of valve plate 40 is controlled as follows. Reference is made to the showings of the valve plate control illustrated at the right-hand end of FIG. 1 and in 7 3 to eventually control the rotary position of the valve plate 40 and the position of the metering slots 42 and 44. The position of the slots relative to the pistons will determine the output capacityof the pump.

It should be noted that the pistons 66 and 68 are of difierent areas. The areas are such that the piston 66 is half that of the piston 68. .However, control pressures of up to 3000 pounds, depending on outlet pressure, are directed by suitable means to the chamber '70 on top of the piston 66 While pressures up to outlet pressure are directed to the chamber '72 on the top of piston 68. A suit able control, which is to regulate the pump output and capacity, meters these pressures to the chambers 70 and 72 to position the racks 62 and 64 and thereby rotate the pinion 60 and the valve plate 40 the desired amount.

With a differential piston arrangement of this type, no actuating springs are necessary and thereby the spring rate errors normally attendant with springs are eliminated.

As a result of this invention, it is apparent that a high capacity output pump can have its capacity substantially reduced while avoiding any hammer and high losses at the low capacity outputs. Of particular importance is the use of a low inertia relief valve which solves a problem not capable ofsolution by .otherrtypes of valves or arrangements. i r

Althoughone'embodiment of this invention has been illustrated and described herein, it will be apparent that various changes may be made in the construction and arrangement of thevarious parts without departing from the scope of the novel concept I claim: v

In an axial piston rotary pump having a plurality of pistons arranged around a common axis and each reciprocable in a path substantially parallel to said axis, a rotor carrying said pistons and rotatable about said axis, re-- I it action means operatively connected to said pistons and fixedly disposed at an angle with respect to said axis whereby said pistons are reciprocated during rotation of said rotor, cylinders for said pistons forming a part of said rotor, said cylinders including openings for conducting the fluid being pumped to and from said cylinders, a disc valve abutting said openings and including a pair of annular slots comprising inlet and outlet ports, a land in said disc defining the closed space between the ends of said slots, passage means having a relier port opening in the face of said land adjacent said openings and com municating with said outlet port, means for rotating said disc valve for varying the pump output such that some of said pistons have their respective cylinder openings crossing said land whereby thepressure in said cylinder openings becomes excessive, a flexible cantilevered member fixed at one end on said disc valve and having a portion of its free end normally covering said relief port, said flexible cantilevered member having one surface in juxtaposition to the disc valve for efi'ectuating damping when the cantilever member moves toward said disc valve, said free end being opened by an excessive pressure buildup in said passage means on the relief port side thereof for relieving fluid from said cylinders. 

